1. Field of the Invention
The present invention relates to a denture base molding apparatus and more particularly to a resin denture base molding apparatus for molding denture bases by injecting fused resin in a plaster mold of a denture base formed in a flask.
2. Description of the Related Art
Conventionally, denture bases have been produced by pressurizing and injecting thermosetting resin such as acrylic resin into a plaster mold of a denture base formed in a flask and by polymerizing and solidifying the resin. However, moldings obtained by such method have less accurate dimensions and less shock resistance as well as less abrasion resistance.
In stead of this method, recently a method for obtaining denture bases having excellent shock resistance and abrasion resistance by injecting thermoplastic resin such as polycarbonate resin into a plaster mold of a denture base formed in a flask is being proposed. That is, in a resin denture base molding apparatus for molding denture bases by injecting thermoplastic resin into a plaster mold of denture base in a flask as shown in FIG. 8, resin R is filled into a cylinder 56 from a through hole 53 and is heated and fused by a heater 57. The apparatus comprises a table 51 for placing flask F provided above a hydraulic press unit 50, two support columns 52 provided on the table 51 and lower and upper support members 54 and 58 provided horizontally to the support columns 52. Then, when a piston rod 61 is lowered by a hydraulic cylinder 59, a resin pressurizing piston 60 is inserted to the cylinder 56 through the through hole 53, pressurizing the resin R. The pressurized resin R is injected to denture base plaster mold S in the flask F from a resin injecting hole 55 through a resin filling hole 62, thereby molding the resin denture base.
In the above apparatus, however, the fused resin R filled in the cylinder 56 sometimes leaks out through the resin injecting hole 55, adheres to the resin filling hole 62 and solidifies and clogs the hole before it is pressurized by the piston 60. Therefore, the resin has to be quickly injected after removing resin R adhered to the resin filling hole 62 by a pincette and the like; it causes a difficulty in the operation.
Furthermore, in order to inject the resin R in high speed, the piston rod 61 has to be driven in high speed, so that the hydraulic press unit 50 for supplying hydraulic pressure to the hydraulic cylinder 59 for driving the piston rod 61 becomes very large. Accordingly, this apparatus has such problems that the whole system becomes heavy and costly.